Wydział Chemii

Natalia Pawlak

Grażyna Oczko

2014

Polyhedron

74

31-38

10.1016/j.poly.2014.02.038

Naukowa

Angielski

Artykuł

Monocrystals of Ln(C₄O₄H₃)₃·8H₂O (Ln = Eu³⁺, Ho³⁺, Er³⁺) were grown and spectroscopic investigations were performed to understand their photophysical properties. It was found that all the complexes were isostructural with neodymium maleate, Nd(C₄O₄H₃)₃·8H₂O, whose crystal structure had been determined previously. Electronic absorption and emission spectra at low temperatures for crystals of the lanthanide maleates (with the splitting of the levels) were allowed for the stated lanthanide ions, with a low symmetry environment, in these systems. The intensities of the electronic lines and the Judd–Ofelt parameters were calculated and compared to those obtained for light lanthanides (i.e. Nd(III) and Sm(III)) maleates. The variation of the spectroscopic parameters (e.g. β, δ) and their correlation with the nature of the Ln³⁺–L bond are discussed. The nephelauxetic ratio β and Sinha’s parameter δ suggested an increase in the ‘degree of covalency’ of the metal–ligand coordination bond from the Eu³⁺ crystal to the Ho³⁺ crystal and to the Er³⁺ crystal of the title compounds. The –CC– double bond in the carboxylate ions determines the distribution of the charge and the character of the Ln–O coordination bonds, which is very important when considering the potential applications of lanthanide carboxylates. In the low-temperature absorption and emission spectra, relatively strong vibronic lines occur, promoted by both ligand (L) and Ln–L localised vibrational modes. In the vibronic coupling, the role of π electrons is not negligible. The emission from the ⁵D₁ level was detected for the europium maleate in spite of the presence of water molecules in the inner coordination sphere of the lanthanide maleate crystals. On the basis of the europium maleate-excited spectra, a ligand-to-metal charge transfer (LMCT) transition was determined at 345 nm.

lanthanides, maleates, UV-Vis spectroscopy, IR spectroscopy

http://dx.doi.org/10.1016/j.poly.2014.02.038

http://www.elsevier.com